I. Field of the Invention
The present invention relates to the fields of oncology, genetics and molecular biology. More particular the invention relates to the overexpression of FJX1 in colon cancer cells, its use as a diagnostic and prognostic marker, and its targeting in colon cancer therapy.
II. Related Art
Colorectal carcinoma (CRC) is the second leading cause of cancer-related deaths in the United States. Currently, it is estimated that there will be approximately 150,000 new cases of CRC and over 56,000 people will die of this disease annually (Jemal et al., 2005; Jemal et al., 2006). While localized tumor growth may cause significant organ dysfunction and even death, metastases cause the vast majority (˜90%) of human cancer deaths (Hanahan and Weinberg, 2000). The ability to metastasize is linked with the ability of cancer cells to invade adjacent tissues, to gain access to vascular or lymphatic channels and to survive their transit so that they may extravasate, then reside and colonize another organ or tissue. Cancer cells acquire the capacity of invasion and metastasis, ultimately due to the interplay of activated oncogenes and loss of tumor suppressor function, but the downstream requisite effectors of these interactions in the regulation of invasiveness and metastasis are incompletely understood. Most lethal cancers are carcinomas; tumors that originate from epithelial cells. Normal epithelial cells exist as well-ordered, immobile, polarized units with controlled and structured cell-cell and cell-matrix junctions. Invasiveness and metastasis in carcinomas involve alterations in the function of cell adhesion molecules such as cadherins and integrins and alterations in expression and activation of extracellular proteases and their inhibitors. Identification of specific effectors of invasiveness and metastasis will provide opportunities for enhanced intervention strategies.
Notch signaling, intestinal development and colorectal cancer. Notch signaling is a highly conserved mechanism of cell-cell communication and regulation of differentiation, proliferation and apoptotic programs during organogenesis and morphogenesis (reviewed in Artavanis-Tsakonas et al., 1999; Wilson and Radtke, 2006). Notch signaling is activated when Deltal-like or Jagged ligands interact with Notch receptors culminating in cleavage of Notch by a presenilin-dependent activity called γ-secretase and release of the Notch Intracellular Domain (NICD). NICD is translocated to the nucleus where it binds to the DNA binding protein RBP-J (also known as CSL (CBF1-human, Su(H)-fly, Lag1-worm) where it displaces RBP-J corepressors and enables transcription of additional transcription factors related to Drosophila hairy and enhancer of split (Hes1, 5, 7 or HERP 1, 2, 3; also known as Hey/Hesr/HRT/CHF/gridlock (FIG. 1). The Hes-related proteins then repress expression of target genes such as Math1, neurogenin (ngn) and Achaete-scute. intera
Notch, Wnt and TGF-β/BMP/Smad signaling in intestinal epithelium. Recent exciting observations have been made regarding the role of Notch in the maintenance of proliferating crypt cells in the normal intestinal epithelium. Regulated Notch signaling in the intestinal crypt is necessary for proper lineage differentiation of intestinal epithelial cells (reviewed in (van Es and Clevers, 2005; Wilson and Radtke, 2006). Activation of Notch signaling in the intestinal epithelium amplifies the proliferating enterocyte progenitor pool and inhibits differentiation (Fre et al., 2005) while inhibition of Notch signaling shuts down crypt progenitor cell proliferation results in goblet cell differentiation (van Es and Clevers, 2005). Inhibition of Notch signaling by pharmacologically blocking γ-secretase activity resulted in induction of Math1 and differentiation into a post-mitotic goblet cell lineage; this phenocopies conditional intestinal Rbp-j gene silencing (van Es and Clevers, 2005). Hes1−/− mice die during embryonic development due to severe neurological abnormalities, but specifically the intestines of the Hes1−/− mice exhibit increased mucous secreting and enteroendocrine cells with relatively fewer absorptive enterocytes (Jensen et al., 2000). Wnt and Notch signaling pathways are simultaneously active in the intestinal crypt of normal epithelium Furthermore, Notch activation is evident throughout the abnormal epithelium of adenomas in ApcMin/+mice (Vooijs et al., 2007) and inhibition of Notch signaling with a γ-secretase inhibitor induces goblet cell differentiation in the adenomas. Thus, Notch signaling is important for normal intestinal epithelial cell proliferation and maintenance of normal distribution of absorptive enterocytes and secretory cells; and when disrupted, differentiation down a secretory pathway and growth arrest occur. Notch signaling with high levels of HES1 and repressed Math1 are necessary for maintaining the proliferative state in colon adenoma cells arising from Wnt signaling activation.
Increased expression of Notch mRNA and proteins has been reported in colon and pancreatic cancers and Jagged is overexpressed in a subset of pancreatic cancers (reviewed in Leong and Karsan, 2006). IKKA associates with specific Notch target gene promoters, releasing SMRT and leading to increased transcription of hes1, hes5, herp2/hrt1 in human colon cancers (Fernandez-Majada et al., 2007). Recent evidence supports important interactions of TGF-β and BMP signaling pathways with Notch and these interactions may have important consequences in development and cancer (Kluppel and Wrana, 2005; Zavadil et al., 2004). Smad3 interacts directly with NICD to activate hes-1 and inhibit myogenic regulatory factors such as MyoD, thus inhibiting differentiation in muscle. Notch is required for BMP mediated inhibition of myogenic differentiation and NICD directly interacts with Smad1 in response to BMP receptor activation. Notch and BMP synergize to activate the hes-related Herp2 in endothelial cells (ECs). When ECs without cell-cell contact are exposed to BMP, Smad1 phosphorylation leads to expression of Id1, an activator of EC migration. On contact with cells expressing Jagged or Delta, Notch is activated leading to synergistic activation of Herp2 which promotes degradation of Id1, thus Herp2 is a negative regulator of migration (Kluppel and Wrana, 2005). Zavadil et al. (2004) recently reported that TGF-β-induced EMT in mouse kidney tubular epithelial cells was accompanied by activation of Hey1 and delayed expression of Jagged 1 in a Smad3 dependent manner. Induction of Hey1 and Jagged were required for TGF-β induced EMT in epithelial cells from kidney, breast and skin. Therefore, normal regulation of Notch, Wnt and TGF-β/BMP signaling are necessary for normal crypt progenitor cell maintenance, proliferation and differentiation. Furthermore, even in the presence of active Wnt signaling, Notch signaling is required for maintenance of the proliferative enterocyte phenotype.
Despite this information, the potential role of Notch, Wnt and TGF-β/BMP/Smad signaling in normal cell development as well as in colorectal cancer cell behavior and tumor progression, remains unclear.